New Genotypes and Diversity of Orientia tsutsugamushi DNA samples from Patients with Scrub Typhus in South Korea as Determined by Multilocus Sequence Typing.

Orientia tsutsugamushi, an obligate intracellular organism, is the causative agent of scrub typhus. Multilocus sequence typing (MLST) is a genetic typing method that provides a unified bacterial isolate characterization approach. However, there are no comparative studies in South Korea on the genotypic properties of O. tsutsugamushi based on MLST. To conduct a comparative analysis with previous data collected from Thailand, Laos, and Japan, we investigated the genetic diversity of O. tsutsugamushi from 51 patients with scrub typhus in South Korea by using MLST. The MLST analysis revealed 10 new alleles in the housekeeping genes: gpsA, n = 2; mdh, n = 1; nrdB, n = 1; nuoF, n = 1; ppdK, n = 1; sucB, n = 2; and sucD, n = 2. These novel alleles led to the assignment of six new sequence types (STs) (ST93-98). The 51 samples corresponded to seven different STs (ST48 and ST93-98), with ST48 accounting for the largest proportion (49.0%) of O. tsutsugamushi STs in South Korea. Interestingly, O. tsutsugamushi from patients with scrub typhus in South Korea were clustered in two different clades, and the five Korean STs (ST48, ST93, ST94, ST95, and ST98) were close genetically to ST80, which was isolated from Laos. The remaining two STs (ST96 and ST97) were close genetically to ST49 (Ikeda, Japan). Overall, our results suggest that the relative genetic stability and the clonal populations of O. tsutsugamushi strains in South Korea have remained mostly conserved.